Nico Rosberg tops times in first practice session

Austin: Nico Rosberg made a determined first move towards wrecking Mercedes teammate Lewis Hamilton's Texan title party when he topped the times in opening free practice for this weekend's United States Grand Prix.

The 30-year-old German, who has to prevent Hamilton beating him by three points in tomorrow's race at the Circuit of the Americas to keep his own challenge alive, clocked a best lap of one minute and 53.989 seconds on a damp, drying track.

Mercedes' Nico Rosberg (centre) talks with a team technician in the pit at the Circuit of The Americas in Austin, Texas before a practice session yesterday. PIC/AFP

Hamilton, feeling his way cautiously, was one of the majority of drivers who were slow to join the fray and wound up fifth quickest after a relatively desultory session in poor conditions.

Heavy rain had soaked the circuit ahead of the action and has been forecast for the rest of the weekend, a factor that may play havoc with the outcome as defending double world champion Hamilton bids to wrap up his third title three races remaining.

Rosberg's best time left him more than 1.2 seconds clear of the Red Bull pairing of Daniil Kvyat and Daniel Ricciardo with Carlos Sainz fourth for Toro Rosso.

Four-time champion Sebastian Vettel, who is second behind Hamilton in the title race, was sixth for Ferrari after clocking only 10 laps in the session. Vettel has already been handicapped ahead of tomorrow's race by being hit with a 10-place grid penalty after Ferrari introduced new engines for the event.

Rosberg completed seven laps in the 90 minutes while Hamilton did only four.